First and foremost, what's your spec? Any warlock who is even mildly interested in raiding will want Improved Shadow Bolt and Bane, as the Shadow Bolt is a key warlock raid spell.
Keeping the fel guard out (as in not sacrificing him) is important, but it's also important to keep him alive, since he's a big part of your damage. Try to group with a shadow priest, Vampiric Embrace really helps with keeping him alive. For most of the raid, turn off the auto casting of all of the fel guard's abilities. On trash, set him on your target, cast Curse of Shadow, Corruption, and then Shadow Bolts. On bosses, turn Cleave back on, cast Corruption, Immolate, Curse of Doom, and Shadow Bolts.
The only time you want to use DS is when you're in a fight that you can not keep the fel guard out for.